Study of metastable NiTi powders and coatings obtained by plasma spraying

NiTi intermetallic is widely known for its shape memory effect and pseudoelasticity. Due to its high corrosion resistanse (biocompatibility), most of the studies carried out deal with its use for medical applications. With regard to surface technologies, many reported investigations focus on Vacuum Thermal Spray to provide NiTi coatings with minimal oxide content. The Thermal Spray Center has attempted to obtain metastable NiTi powders and coatings by means of Atmospheric Plasma Spraying with a liquid nitrogen cooling system. Starting from two different Ni-45wt%Ti feedstock powders. One powder is a blend of Ti and Ni particles, whereas the other has been alloyed by gas atomization. Both powders were sprayed obtaining better results starting from the gas atomized powder resulting in a final deposit where NiTi was the main phase with minimal oxidation. Different spraying parameters were tested and microstructural characterization was performed by SEM-EDS. XRD patterns showed some peak broadening; that seems to be produced by structural metastability of the coatings.